1. Field of the Invention
The present invention relates to a two-stage isolated DC/AC conversion circuit structure, in particular, to a circuit design able to reduce the capacity value of the DC link output capacitor, to use a capacitor with smaller capacitance and avoid using an electrolytic capacitor with large capacitance but a short lifespan, so as to increase the service life of the circuit, and the later stage AC converter able to operate in low-frequency switching, which not only reduces the switching losses and the impact of dead time, and improves circuit efficiency, but also reduces the circuit volume and cost, thereby increasing the converter's working life, and when the converter operates in a grid connected operation mode, it can be seamlessly controlled in grid connected operation mode through circuit design and control.
2. Description of Related Art
Conventional DC/AC converters, as in Taiwan patent application serial No. 092200019, (improved structure of a DC to AC converter) disclose the following: a switch circuit, this switch circuit is a bridge type switch circuit, with one end having a DC power supply, and the AC end is connected in series to the storage inductor, and again connected to a side end of the transformer input; one transformer, the other end of the input side again connected to the other AC end of the electric switch, and the second AC end of the switch circuit is situated respectively on the second diode; one integrated circuit, the input end connected to the second diode, and the output end then connected to the pulse width modulation controller on the feedback end ; one pulse width modulation controller, the reference electric potential end is connected to the waveform generator, to input the sine waves of the waveform generator; one waveform generator, to generate half cycle sine waves, and to generate low frequency square waves to supply the control driver circuit, one control driver circuit, to calculate the output of the pulse width modulation controller and the low frequency square waves generated by the waveform generator, and to provide the control signals required by the switch circuit.
In a conventional DC/AC converter, even though the DC electricity of the DC power supply only passes a group of switch circuits and one transformer, it can convert the electricity and output an AC, simplify the circuit structure, and can also improve its reliability and save costs. But this circuit structure is still complex, and the cost of the many used electrical components is high, and it doesn't possess isolation effects, and can't prevent all the stored energy for the later stage electricity end user recharging to the front stage DC/AC converter electric circuit, which results in damaged circuits. From this you will notice the above conventional device has many drawbacks, is not well designed, and is waiting for improvement.
Therefore looking at the flaws and drawbacks of the above described conventional DC/AC converter, this inventor was eager to improve on the innovation, and after many years of painstaking research has finally successfully researched and developed this kind of two-stage isolated DC/AC converter electric circuit structure.